Radio frequency identification (RFID) tag lamination process

ABSTRACT

A method of constructing an RFID unit can include using a protective layer to hold an integrated circuit chip module to a substrate layer with an antenna unit while a conductive adhesive has not yet fully set.

BACKGROUND OF INVENTION

Radio Frequency Identification (RFID) tags are typically small objectsthat can be attached to or incorporated into a product. RFID tagscontain antenna to enable them to receive and respond to radio-frequencyqueries from an RFID tranciever. The RFID tags are used in a host ofindustries for purposes such as inventory control, security, personalidentification and the like.

The RFID tags can be passive or active. Active devices have their ownpower supply. Passive devices rely on energization from the RFIDtranciever. Passive and active RFID tags can use integrated circuitchips to modulate the identification response.

The construction of RFID units can consist of the attachment of a chipmodule to a substrate with an antenna unit. The chip module is typicallyattached to the substrate with an electrically conductive adhesive andthen the combined unit can be further processed after the adhesive sets.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of an RFID unit of one embodiment.

FIG. 2 is a top view of an RFID unit of one embodiment.

FIG. 3 is a diagram of an apparatus to construct an RFID unit of oneembodiment.

DETAILED DESCRIPTION

One embodiment of the present invention comprises a method ofconstructing an RFID unit. The method comprises attaching an integratedcircuit chip to a substrate with an antenna unit using an adhesive; andlaminating a protective layer over at least a portion of the integratedcircuit chip while the adhesive has not yet fully set.

FIG. 1 illustrates a cross section diagram of an RFID unit 100 of oneembodiment. In this embodiment, the integrated circuit 102 is part of amodule 104 which also includes lead frame elements 106 and 108. Otherconnection elements other than a lead frame could be used in the module104. The module 104 is adhesively connected to substrate 110 includingantenna elements 112 and 114 using a conductive adhesive 116. Theconductive adhesive 116 can be a conventional isotropic conductiveadhesive, and anisotropic conductive adhesive or even solder such assolder paste.

FIG. 2 illustrates a top view where module 202 with IC 204 and leadframe 206 and 208 are connected using the conductive adhesive to theantenna unit 210 to form the RFID unit 200.

Looking again at FIG. 1, the protective layer 120 can be laminated overthe module 104 including the integrated circuit 102. The protectivelayer 120 can hold the module 102 in place while the conductive adhesive116 sets.

The laminating protective layer can be made of many type of materialsincluding thermoplastic material, thermoset material, polyester,polystyrene, polypropylene, polyethylene. The protective layer may havean adhesive layer. In one embodiment, the protective layer is relativelystretchy and will conform the shape of the module or integrated circuitchip. In one embodiment, since the lamination is done before theadhesive is fully set, there does not have to be any dwell time betweenattaching and laminating steps. In one embodiment, the dwell time can bereduced below a minute. The attachment step can be done at a high ratedue to the lack of requirement for the conductive adhesive to fully set.In one embodiment, the attachment is done at a rate of one attachmentper second or greater. The conductive adhesive can be of such that ittakes a long time to fully set since the protective layer holds themodule in place. Thus, the conductive adhesive can take over a day tofully set, which can greatly increase the pot time of the adhesive inthe apparatus to produce the RFID units.

The protective layer can have a radiation or heat curable adhesive. Inone embodiment, the protective layer has an ultra violet (UV) curableadhesive that can be cured in a later step.

FIG. 3 illustrates an apparatus of one embodiment. In this embodiment,the laminating protective layer is held in a strip on roll 302. If theprotective layer has a liner it can be removed onto roll 304. A roll 305containing a strip with chip modules can feed to device 307 which canattached the chip module up side down on the protective layer 308. Theantenna material can be a strip on roll 310. The conductive adhesive canbe provided by an adhesive dispenser 314 to dispense upon module, suchas on the leadframe of the module. An attachment unit 316 attaches theprotective layer 308 with modules to the antenna material strip 309.Dancers 320 and 321 can be used to register the substrate strip havingantenna units with the modules on the protective layer 308. A laminationunit 322 can later be used to laminate the protective layer over theintegrated circuit chip module. The finished material can be rolled upinto a roll 324 which can be held for later processing. The laterprocessing can include cure step which can be done at a separatelocation from the apparatus 300. The laminating unit 322 can use hotrollers. The attaching unit 316 can operate at a rate greater than oneattachment per second or greater.

In the example of FIG. 3, the integrated circuit chip (as part of thechip module) is attached to the protective layer before the attachingunit. This need not be the case, but it can allow the chips to be spacedon a strip such that the chips will register in position with thesubstrate strip having the antenna unit. In an alternate embodiment, theintegrated circuit chip, as part of the chip module, is attached to thesubstrate with antenna first followed by the lamination of theprotective layer.

One embodiment of the present invention is a method of constructing anRFID unit comprising using a conductive adhesive to attach an integratedcircuit chip module to a substrate with an antenna unit; and laminatinga protective layer over at least a part of the integrated circuit chipmodule while the conductive adhesive has not yet fully set.

One embodiment of the present invention is a method of constructing anRFID unit comprising placing a integrated circuit chip module on aprotective layer, wherein the protective layer includes an adhesive tohold the integrated circuit module; placing a conductive adhesive on atleast portions of the integrated circuit chip module; and attaching theintegrated circuit chip module to a substrate with an antenna unit.

One embodiment of the present invention is an RFID unit comprising asubstrate with an antenna unit; an integrated circuit chip to thesubstrate with an antenna unit using an adhesive; and a protective layerlaminated over at least a part of the integrated circuit chip while theadhesive has not yet fully set.

The chip module can be a single chip attached to a lead frame orsuitable substrate with appropriate electrical connections forattachment to the antenna-examples of chip modules are offered byPhilips Electronics, Netherlands (FCP package) and Alien Technologies ofMorgan Hill Calif. (Alien Strap) The lead frame can terminates in twopads, which are intended to attach to the RFID circuit by a conductiveadhesive. Chip modules can be utilized in order to alleviate thedifficulties that normally arise when placing a small integratedcircuits (typical integrated circuits are <1 mm square, and the arealdensity of integrated circuits are typically very low, <0.25units/square inch). In traditional application, the mounting of smallintegrated circuits without a leadframe leads to low process throughputowing to the time delay inherent in locating and placing such a smallintegrated circuit.

The disadvantages of previous processes relate to process throughput andreliability. Application of non-conductive epoxy under the integratedcircuit and conductive epoxy to the outer leads results in amechanically and electrically reliable assembly, however the dwell timefor the circuit, i.e. that time that the circuit must be immobilizedwhile the adhesives cure is typically several minutes. This may bedecreased by using faster curing epoxy resins however the inherentchemical instability of so-called snap cure resins makes handlingdifficult and leads to excessive yield loss or high material wastage.Anisotropic adhesives, either tapes or pastes offer increased throughputwith respect to epoxy adhesives however the dwell time per attachment istypically several seconds and during the dwell time the module must beheld immobile on the substrate using considerable pressure to effect areliable electrical connection. The use of a laminated protective layercan produce a throughput in excess of one attachment per second thatinsures mechanical stability of the device. The equipment can berelatively simple to maintain a very low cost of ownership of theoverall process. This can be as low as $0.01 or less per attachment whenconsidering the overall cost of materials and equipment amortization.

In one embodiment, a traditional conductive adhesive can be placed overthe terminals of the circuit to which the module is to be attached orplaced on the terminals of the module prior to assembly.

The module can be placed on the substrate with contact of the terminalsof the module on the appropriate terminal of the circuit. Alternatively,the module may be temporarily attached to a tape which is subsequentlylaminated to the circuit.

A protective layer can be laminated over the module of a tape whichholds the module in place while the adhesive is cured (partially orfully). The tape may held in place by a variety of adhesives includingan adhesive selected from any of a number of adhesive types; hot melt,pressure sensitive, UV cure, thermoset etc. This laminate may cover themodule fully or partially or it may be advantageous to use a segmentedor multiple adhesives for specific uses.

A curing step can be done to set, such as cure, the conductive adhesive.This step may be of a type that initiates cure of the adhesive whichproceeds after the circuit has been removed from the immediate vicinityof the attachment and/or curing station.

The protective layer can form a protective cover for the module,particularly if the laminate conforms closely to the shape of the moduleafter lamination. There is no requirement for dwell time in theplacement equipment. This means that parts with a partially curedadhesive can be safely rolled up and stored while the curing processtakes place. This has the dual benefit of increasing process throughputand reducing material waste costs. Tape lamination equipment presentlyavailable can be modified to suit this application. The throughput ofexiting equipment is sufficient to meet the imperative of a low costhigh throughput process for placement and attachment of the module.

In alternate embodiments, a curable adhesive can be placed over themodule contemporaneously with the conductive adhesive; an anisotropicadhesive can be used rather than traditional conductive adhesive; and/oran anisotropic adhesive can be used in place of both the traditionalconductive adhesive and a laminating adhesive.

An alternate embodiment is a method for constructing a flexible circuitcomprising attaching an integrated circuit chip to a substrate with ancircuit traces using an adhesive; and laminating a protective layer overat least part of the integrated circuit chip while the adhesive has notyet fully set.

The foregoing description of preferred embodiments of the presentinvention has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Many embodiments were chosenand described in order to best explain the principles of the inventionand its practical application, thereby enabling others skilled in theart to understand the invention for various embodiments and with variousmodifications that are suited to the particular use contemplated. It isintended that the scope of the invention be defined by the claims andtheir equivalents.

1. A method of constructing an RFID unit comprising: attaching an integrated circuit chip to a substrate with an antenna unit using an adhesive; and laminating a protective layer over at least part of the integrated circuit chip while the adhesive has not yet fully set.
 2. The method of claim 1, wherein the integrated circuit chip is part of a chip module.
 3. The method of claim 2, wherein the chip module includes a lead frame.
 4. The method of claim 2, wherein attaching step comprises using the adhesive to connect a connection element of the module to the substrate.
 5. The method of claim 1, wherein any dwell time between the attaching and laminating steps is less than less than minute.
 6. The method of claim 1, wherein the attachment step is done at a rate of one attachment per second or greater.
 7. The method of claim 1, wherein the adhesive takes over a day to fully set.
 8. The method of claim 1, wherein the adhesive is an electrically conductive adhesive.
 9. The method of claim 8, wherein the conductive adhesive is solder paste.
 10. The method of claim 1, wherein the integrated circuit chip is attached to the protective layer before the attaching step.
 11. The method of claim 1, wherein the protective layer is stretchy to conform to IC chip.
 12. An apparatus to construct an RFID unit comprising: a unit to attach an integrated circuit chip to a substrate with an antenna unit using an adhesive; and a unit to laminate a protective layer over at least part of the integrated circuit chip while the adhesive has not yet fully set.
 13. The apparatus of claim 12, wherein the integrated circuit chip is part of a chip module.
 14. The apparatus of claim 12, wherein the laminating unit connects a strip of the protective layer to a strip of the substrate.
 15. The apparatus of claim 12, wherein the laminating unit uses hot rollers.
 16. The apparatus of claim 12, wherein the attaching unit operates at a rate of one attachment per second or greater.
 17. The apparatus of claim 12, wherein the integrated circuit chip is attached to the protective layer before the attaching unit.
 18. A method of constructing an flexible circuit comprising: attaching an integrated circuit chip to a substrate with an circuit traces using an adhesive; and; laminating a protective layer over at least part of the integrated circuit chip while the adhesive has not yet fully set. 